A vehicle air bag module typically includes a container, which has an open side and encloses a gas generator and at least part of an air bag, and a cover which closes the container. When the air bag module is designed for the passenger side of a vehicle, the container may be located just behind the vehicle dashboard, and the cover may form an integral part of the vehicle dashboard.
When the vehicle is involved in a collision, a crash signal initiates operation of the gas generator to cause the air bag to deploy. Specifically, the gas generator produces an inert gas (e.g., nitrogen) which is directed under pressure against the air bag to force the air bag out of the container incorporated in the module and into the passenger compartment. As the air bag is forced out of the container, the pressure exerted on the cover causes selected portions of the cover to separate, in a predetermined manner, to enable the air bag to be directed into the passenger compartment. As the air bag is directed into the passenger compartment, it is inflated by the continued flow of gas produced by the gas generator.
During deployment of an air bag, the container, which is generally made of metal (e.g., steel sheet), must withstand significant pressures. More specifically, a passenger side gas generator when actuated, is believed to produce gas pressure of approximately 10-40 psi in the container. It has been found that under such pressure the central part of the module container, in the vicinity of its opening, may tend to bulge or "fishmouth" outward during deployment of the air bag. When the opening of the air bag container is located adjacent the vehicle dashboard, bulging of the central part of the container can crack (or deform) the dashboard, thereby requiring replacement of the entire dashboard.
A known technique for reinforcing the opening of a metal air bag container is to bend the metal located around the opening in an outward direction to reinforce the opening. One undesirable result of bending the metal around the container opening in an outward direction is that the container opening is enlarged. Enlarging the container opening also enlarges the module, which is undesirable in today's vehicles, where minimizing the dimensions of the module is an important criterion. Additionally, in the applicants' experience, bulging of the central part of the container is still possible even if the container is reinforced around the opening by bending the metal outward. Thus, there has been a need to address the problem of bulging or fishmouthing of the central part of the container around its opening, while minimizing the dimensions of the air bag module.
In addition, in assembling an air bag module, it is important that the air bag be folded into the container in a manner which allows the bag to be effectively deployed without risk of snagging or other interference. Accordingly, internal reinforcement of the container has heretofore been an unattractive alternative to designers of air bag modules.